Oidiodendron maius is accepted widely as an ericoid mycorrhizal endophyte because it is isolated primarily from the roots of ericaceous plants. Reports of the species from other materials are much fewer, suggesting a limited role as a free-living saprobe. We show that assumptions concerning the prevalence of O. maius in a common substrate (i.e. peat) are affected by isolation protocols. Oidiodendron maius was observed on 99.6% of peat samples incubated in moist chambers but only 0–9% of the peat fragments plated on different isolation media. These results, and previous studies showing ability to degrade Sphagnum, indicate that O. maius could inhabit a much broader niche than previously suspected. Sterile ascocarps with peridia morphologically similar to Myxotrichum arcticum were observed on moist incubated peat and in a series of controlled crosses. These observations provide evidence that the teleomorph of O. maius is a species of Myxotrichum.